For example, Japanese Laid-Open Patent Application No. 2008-172292 discloses the following technology of identifying the location of a failure in a network. When a failure occurs, information relevant to the network is deleted from a MAC learning table. However, before deleting the information, the information is saved in a storage unit. A link trace function is implemented for transmitting and receiving link trace signals with ports by referring to the saved information. Accordingly, the location of the failure is identified.